Thousands of people have gathered at Ground Zero in New York City, as the families of the victims commemorate the attack on the World Trade Center for a seventh year.

The crowd observed two moments of silence Thursday, at 8:46 a.m. and 9:03 a.m., to mark the exact times two hijacked airliners crashed into the center's twin towers.

The relatives, some holding back tears, paired with students from 90 countries and read names of the victims. As each name was read, other relatives placed a flower in one of two small reflecting pools. The students represented the homelands of victims.

Near Washington, a lone bagpiper played "Amazing Grace" as he walked through rows of empty benches at a new Pentagon memorial.

The 184 benches, draped in blue shrouds with American flags before the memorial was unveiled, each represent a victim of the attack on the Pentagon, those in the building and those on board the hijacked plane that crashed into the building's western wall.

Each bench has the name of one of the victims. Benches with the names of those killed in the Pentagon point toward the building. Benches with the names of those on board the hijacked plane point in the opposite direction, toward the sky.

A sailor at the Pentagon also rang a bell, one ring for each victim.

At the New York Stock Exchange, in the center of the city's financial district, investors also held a moment of silence to remember their colleagues who were killed in the attack on the World Trade Center.